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In a terminal, please run the following and paste the results back here:
lspci -vnn -s $(lspci | fgrep -i network | cut -d" " -f1)
This will give us the hardware you are running.
Generally, the older ralink chips have a driver supplied in the staging area,
/lib/modules/2.6.32-39-generic/kernel/drivers/staging/rt2860/rt2860sta.ko
which works (but works better with wicd instead of network-manager because wicd
reconnects faster after dropouts). A config file may be missing -- /etc/Wireless/RT2860STA/RT2860STA.dat which is a part of the source download from the vendor -- Since the legal channels are set in that file, not sure how the device runs without it, but I think it might.
Since Ubuntu 11.04, the rt2900pci driver handles the older ralink chips, and the vendor driver is not needed except for newer chips. Check the blacklisted drivers in /etc/modules.d/* and make sure you only have either the ralink driver or the rt2800pci driver, not both.

Please first connect your wired network adapter to the wireless router using an ethernet cable (also known as a LAN cable).

In order to gather essential troubleshooting information about your wireless card, please follow this procedure:

Step 1:

If you are using the Gnome interface, open the Terminal console via "Applications->Accessories->Terminal"

If you are using the Unity interface, the easiest way to open the Terminal is to use the 'search' function on the dash. Or you can click on the 'More Apps' button, click on the 'See more results' by the installed section, and find it in that list of applications. A third way, available after you click on the 'More Apps' button, is to go to the search bar, and see that the far right end of it says 'All Applications'. You then click on that, and you'll see the full list. Then you can go to Accessories > Terminal after that.

Step 2: Please copy-paste the following command from https://help.ubuntu.com/community/WirelessTroubleshootingProcedure in Firefox into the Linux Terminal. Do NOT copy-paste from the Email message into the Terminal, as that will only copy PART of the command. The command STARTS with the word sudo and ENDS with the word lsmod. So please copy-paste the ENTIRE command below from Firefox into a Terminal, press <enter>, then enter password when sudo asks for password, then press enter again.

Tip: If you have a wheel mouse or 3 button mouse you do not need to type commands into the Terminal. Highlight the command written on the page. Move your cursor anywhere in the Terminal and press the wheel or middle button. Automatic Copy and paste! No spelling mistakes! No Typos! No other errors!

Display options:
-v Be verbose (-vv for very verbose)
-k Show kernel drivers handling each device
-x Show hex-dump of the standard part of the config space
-xxx Show hex-dump of the whole config space (dangerous; root only)
-xxxx Show hex-dump of the 4096-byte extended config space (root only)
-b Bus-centric view (addresses and IRQ's as seen by the bus)
-D Always show domain numbers

Please first connect your wired network adapter to the wireless router using an ethernet cable (also known as a LAN cable).

In order to gather essential troubleshooting information about your wireless card, please follow this procedure:

Step 1:

If you are using the Gnome interface, open the Terminal console via "Applications->Accessories->Terminal"

If you are using the Unity interface, the easiest way to open the Terminal is to use the 'search' function on the dash. Or you can click on the 'More Apps' button, click on the 'See more results' by the installed section, and find it in that list of applications. A third way, available after you click on the 'More Apps' button, is to go to the search bar, and see that the far right end of it says 'All Applications'. You then click on that, and you'll see the full list. Then you can go to Accessories > Terminal after that.

Step 2: Please copy-paste the following command from https://help.ubuntu.com/community/WirelessTroubleshootingProcedure in Firefox into the Linux Terminal. Do NOT copy-paste from the Email message into the Terminal, as that will only copy PART of the command. The command STARTS with the word sudo and ENDS with the word lsmod. So please copy-paste the ENTIRE command below from Firefox into a Terminal, press <enter>, then enter password when sudo asks for password, then press enter again.

Tip: If you have a wheel mouse or 3 button mouse you do not need to type commands into the Terminal. Highlight the command written on the page. Move your cursor anywhere in the Terminal and press the wheel or middle button. Automatic Copy and paste! No spelling mistakes! No Typos! No other errors!

Nothing wrong with the command, even a cut and paste from your email worked on my system. Try Mark's script, that'll give all the info we need. Possible issues with the command are 1) no cut command!!! unlikely, that is in coreutils and is always present, 2) running a non-bash shell (or older bash?), ...

"Martin Pitt wrote on 2010-06-09: #10
Accepted linux-firmware into lucid-proposed, the package will build now and be available in a few hours. Please test and give feedback here. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you in advance!"

If all those steps still do not help, then change wireless encryption from WPA (or WPA2) to WEP encryption, as suggested here